Sully, besmirch (6)
I believe the answer is:
This clue is a double definition.
'sully' is the first definition.
(I know that sully can be written as defile)
'besmirch' is the second definition.
(I've seen this in another clue)
(Other definitions for defile that I've seen before include "Make dirty in narrow gorge" , "Contaminate" , "Befoul" , "Narrow pass; pollute" , "Soil" .)